A detector system of the above kind is, for example, described in the article of Ute Golla in the Journal of Microscopy, Volume 173 (1999), pages 219 to 225. A disadvantage in this known detector system is that only image information can be detected in the bright field contrast, that is, only electrons are detected which were scattered elastically at the specimen.
A further system for generating transmission images in a scanning electron microscope is described in U.S. Pat. No. 6,815,678. This system comprises a specimen holder or several specimen holders below which a diaphragm is mounted. This diaphragm is movable relative to the specimen holders. The electrons, which are transmitted through the diaphragm, are subsequently detected. Because of the relative shift between the diaphragm and the primary electron beam or the specimen, different contrasts can be generated, especially, image data can be recorded which corresponds to a bright field contrast, a dark field contrast or a mix thereof.
A detector system for an environmental scanning electron microscope (ESEM) is disclosed in U.S. Pat. No. 4,897,545. This electron microscope is designed for operation at a relatively high pressure in the specimen chamber. The detector system comprises several annularly-shaped and segmented electrodes. These detectors function to generate a direction-dependent topographical contrast of the specimen irradiated by the primary electron beam.
U.S. Pat. No. 3,908,124 discloses a scanning electron microscope which has below the specimen two detectors which are arranged offset to each other in the beam direction of the primary electron beam. The detector at the specimen side includes a central disc-shaped or decentral ring-shaped aperture. Electrons, which are transmitted through the specimen, or electrons, which are scattered by the specimen in the forward direction, can pass the detector at the specimen side through the aperture and impinge upon the second detector lying therebehind. An image datum can be generated via difference formation of the two detector signals which corresponds to a phase contrast.